Section 29.917

14 CFR Ch. I (1-1-19 Edition)

(2) Each fan is located so that a fan
blade failure will not jeopardize safety;
or
(3) Each fan blade can withstand an
ultimate load of 1.5 times the centrifugal force expected in service, limited by either - 
(i) The highest rotational speeds
achievable under uncontrolled conditions; or
(ii) An overspeed limiting device.
(c) Fatigue evaluation. Unless a fatigue evaluation under Section 29.571 is conducted, it must be shown that cooling
fan blades are not operating at resonant conditions within the operating
limits of the rotorcraft.
(Secs. 313(a), 601, and 603, 72 Stat. 752, 775, 49
U.S.C. 1354(a), 1421, and 1423; sec. 6(c), 49
U.S.C. 1655 (c))
[Amdt. 29-13, 42 FR 15046, Mar. 17, 1977, as
amended by Amdt. 29-26, 53 FR 34215, Sept. 2,
1988]

spaschal on DSK3GDR082PROD with CFR

ROTOR DRIVE SYSTEM
Section 29.917 Design.
(a) General. The rotor drive system
includes any part necessary to transmit power from the engines to the
rotor hubs. This includes gear boxes,
shafting, universal joints, couplings,
rotor brake assemblies, clutches, supporting bearings for shafting, any attendant accessory pads or drives, and
any cooling fans that are a part of, attached to, or mounted on the rotor
drive system.
(b) Design assessment. A design assessment must be performed to ensure that
the rotor drive system functions safely
over the full range of conditions for
which certification is sought. The design assessment must include a detailed failure analysis to identify all
failures that will prevent continued
safe flight or safe landing and must
identify the means to minimize the
likelihood of their occurrence.
(c) Arrangement. Rotor drive systems
must be arranged as follows:
(1) Each rotor drive system of multiengine rotorcraft must be arranged so
that each rotor necessary for operation
and control will continue to be driven
by the remaining engines if any engine
fails.
(2) For single-engine rotorcraft, each
rotor drive system must be so arranged

that each rotor necessary for control in
autorotation will continue to be driven
by the main rotors after disengagement of the engine from the main and
auxiliary rotors.
(3) Each rotor drive system must incorporate a unit for each engine to
automatically disengage that engine
from the main and auxiliary rotors if
that engine fails.
(4) If a torque limiting device is used
in the rotor drive system, it must be
located so as to allow continued control of the rotorcraft when the device
is operating.
(5) If the rotors must be phased for
intermeshing, each system must provide constant and positive phase relationship under any operating condition.
(6) If a rotor dephasing device is incorporated, there must be means to
keep the rotors locked in proper phase
before operation.
[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as
amended by Amdt. 29-12, 41 FR 55472, Dec. 20,
1976; Amdt. 29-40, 61 FR 21908, May 10, 1996]

Section 29.921 Rotor brake.
If there is a means to control the rotation of the rotor drive system independently of the engine, any limitations on the use of that means must be
specified, and the control for that
means must be guarded to prevent inadvertent operation.
Section 29.923 Rotor drive system and control mechanism tests.
(a) Endurance tests, general. Each
rotor drive system and rotor control
mechanism must be tested, as prescribed in paragraphs (b) through (n)
and (p) of this section, for at least 200
hours plus the time required to meet
the requirements of paragraphs (b)(2),
(b)(3), and (k) of this section. These
tests must be conducted as follows:
(1) Ten-hour test cycles must be used,
except that the test cycle must be extended to include the OEI test of paragraphs (b)(2) and (k), of this section if
OEI ratings are requested.
(2) The tests must be conducted on
the rotorcraft.
(3) The test torque and rotational
speed must be - 
(i) Determined by the powerplant
limitations; and

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